Chip type variable electronic part and chip type variable resistor

ABSTRACT

In a chip type variable electronic part including an insulating substrate, and an adjustment rotor made of a metal plate rotatably mounted on an upper surface of the insulating substrate, in which the rotor is constituted of a first plate formed in a bowl shape to receive a screwdriver that rotates the rotor, and a second plate superposed on an upper surface of the first plate and integrally coupled thereto via a fold-back joint, and the second plate includes a screwdriver engagement hole perforated therein for the screwdriver to be fitted in, the fold-back joint includes a pair of left and right downwardly bent lugs formed between a bending line of the fold-back joint and the second plate, such that a portion of the fold-back joint between the bending line thereof and the first plate is fitted between the pair of downwardly bent lugs, thereby preventing deformation of the fold-back joint when the rotor is rotated with the screwdriver.

TECHNICAL FIELD

The present invention relates to a chip type variable electronic part ora variable resistor constituted of an insulating substrate in the formof a chip, with a rotor for controlling the resistance value orcapacitance that is rotatably mounted on an upper surface of thesubstrate.

BACKGROUND ART

The chip type variable resistor which represents the variable electronicparts includes, as described in patent document 1 and as conventionallywell known, an insulating substrate formed in a chip type with a throughhole provided at a central portion thereof, a resistance film providedon an upper surface thereof in an arcuate shape concentric with thethrough hole, an external terminal electrode corresponding to therespective end portions of the arcuate resistance film provided on theinsulating substrate, and an internal terminal electrode plate made of ametal plate adhered to a lower surface of the insulating substrate andincluding an integrally formed shaft portion that fits in the throughhole. On the upper surface side of the insulating substrate, anadjustment rotor made of a metal plate is rotatably mounted on an upperend portion of the shaft portion, and the rotor is constituted of afirst plate formed in a bowl shape to receive a screwdriver that rotatesthe rotor, and a second plate superposed on an upper surface of thefirst plate and integrally coupled thereto via a fold-back joint. Thefirst plate is provided with a sliding piece held in contact with theresistance film, and a screwdriver engagement hole in which thescrewdriver is to be fitted is perforated in the second plate.

Also, in the conventional chip type variable resistor, as described inthe patent document 1, an internal terminal electrode plate disposed onthe lower surface of the insulating substrate is provided with a stopperpiece formed to project upward from the upper surface of the insulatingsubstrate, so that when the rotor rotates the fold-back joint of therotor is butted to the stopper piece, and a rotation angle of the rotoris thereby delimited.

In the foregoing chip type variable resistor, the adjustment rotor is,as already stated, constituted of the first plate formed in a bowl shapeto receive the screwdriver that rotates the rotor, and the second platesuperposed on the upper surface of the first plate and integrallycoupled thereto via the fold-back joint, in which the first plate isprovided with the sliding piece held in contact with the resistancefilm, and the screwdriver engagement hole in which the screwdriver is tobe fitted is perforated in the second plate. In other words, rotatingthe second plate with the screwdriver inserted in the screwdriverengagement hole perforated therein causes the first plate provided withthe sliding piece held in contact with the resistance film to rotate,with the sliding piece provided thereto maintained in contact with theresistance film, and hence the torsional torque required to rotate thefirst plate is also applied to the fold-back joint connecting the firstplate and the second plate, which leads to a problem that when rotatingthe rotor with the screwdriver, the fold-back joint of the rotor isdeformed such that the first plate and the second plate are shifted fromeach other.

For this reason, the patent document 1 proposes increasing a widthwisedimension of the fold-back joint for preventing the deformation, howeverincreasing the width of the fold-back joint not only makes the foldingwork of the fold-back joint more difficult but also incurs an increasein weight, and besides when delimiting the rotation angle of the rotorby blocking the fold-back joint with the stopper piece, the rotationangle range is reduced to the same extent as the increase in width ofthe fold-back joint.

Also, for delimiting the rotation angle of the rotor the fold-back jointis butted to the stopper piece, and hence the stopper piece has to havea sufficient projecting height from the upper surface of the insulatingsubstrate to reach the fold-back joint, which incurs a problem that astrength of the stopper piece is reduced against tilting in a rotationdirection of the rotor thus being deformed, caused by the rotationthereof.

To increase the strength of the stopper piece against tilting, awidthwise dimension thereof may be increased in a rotation direction ofthe rotor, however increasing the width of the stopper piece not onlyincurs an increase in weight, but also results in reduction in rotationangle of the rotor, to the same extent as the increase in width of thestopper piece.

Patent document 1: JP-A-H11-354307

DISCLOSURE OF THE INVENTION Problem to be Solved by the Invention

A technical object of the present invention is to provide a chip typevariable electronic part and a variable resistor in which the foregoingproblems are minimized.

Means for Solving the Problem

To achieve the technical object, a first aspect of the present inventionprovides a chip type variable electronic part including an insulatingsubstrate and an adjustment rotor made of a metal plate rotatablymounted on an upper surface of the insulating substrate; in which therotor is constituted of a first plate formed in a bowl shape to receivea screwdriver that rotates the rotor, and a second plate superposed onan upper surface of the first plate and integrally coupled thereto via afold-back joint, and the second plate includes a screwdriver engagementhole perforated therein for the screwdriver to be fitted in; wherein thefold-back joint includes a pair of left and right downwardly bent lugsformed between a bending line of the fold-back joint and the secondplate, such that a portion of the fold-back joint between the bendingline thereof and the first plate is fitted between the pair ofdownwardly bent lugs.

A second aspect of the present invention provides the chip type variableelectronic part according to the first aspect, wherein the pair ofdownwardly bent lugs extends farther downward from a lower surface ofthe portion of the fold-back joint between the bending line thereof andthe first plate, to be butted to a stopper piece projecting upward froman upper surface of the insulating substrate.

A third aspect of the present invention provides the chip type variableelectronic part according to the second aspect, wherein the stopperpiece is an upwardly bent portion of an internal terminal electrodeplate disposed on a lower surface of the insulating substrate.

A fourth aspect of the present invention provides the chip type variableelectronic part according to the third aspect, wherein the stopper pieceincludes an abutment portion integrally formed therewith, to be incontact with the upper surface of the insulating substrate.

A fifth aspect of the present invention provides the chip type variableelectronic part according to any of the first to the fourth aspects,further comprising, on the insulating substrate, a resistance film of anarcuate shape concentric with the through hole; and an external terminalelectrode corresponding to the respective end portions of the resistancefilm; wherein the adjustment rotor includes a sliding piece held insliding contact with the resistance film.

ADVANTAGE OF THE INVENTION

Since the fold-back joint includes, as described in the first aspect, apair of left and right downwardly bent lugs formed between a bendingline of the fold-back joint and the second plate, such that a portion ofthe fold-back joint between the bending line thereof and the first plateis fitted between the pair of downwardly bent lugs, a rotational forceapplied to the second plate by a screwdriver inserted in the screwdriverengagement hole is transmitted to the first plate via the downwardlybent lug, which reliably prevents the deformation of the fold-backjoint, without an increase in width of the fold-back joint, and hencewithout incurring greater difficulty in performing the bending work ofthe fold-back joint, and without incurring an increase in weight of therotor, and reduction in rotation angle thereof.

Also, as described in the second aspect, the pair of downwardly bentlugs extends farther downward from a lower surface of the portion of thefold-back joint between the bending line thereof and the first plate, tobe butted to a stopper piece projecting upward from an upper surface ofthe insulating substrate, which allows forming the stopper piece in alower projecting height from the upper surface of the insulatingsubstrate than in the case where the fold-back joint is butted to thestopper piece, thereby effectively increasing the strength of thestopper piece against tilting in the rotation direction of the rotorthus being deformed, without an increase in width of the stopper piece,and hence without incurring an increase in weight of the rotor, andreduction in rotation angle thereof.

Further, since the stopper piece is an upwardly bent portion of aninternal terminal electrode plate disposed on a lower surface of theinsulating substrate as described in the third aspect, the formation ofthe stopper piece can be easily carried out utilizing the internalterminal electrode plate.

In this case, since the stopper piece includes an abutment portionintegrally formed therewith, to be in contact with the upper surface ofthe insulating substrate as described in the fourth aspect, theinsulating substrate is held by the stopper piece from an upper and alower direction, which leads to a further increase in strength of thestopper against tilting in the rotation direction of the rotor, and toreinforced adhesion of the internal terminal electrode plate to theinsulating substrate.

Especially, the configuration according to the fifth aspect isadvantageous in effectively achieving the foregoing effects in the chiptype variable resistor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view showing a variable resistor according to anembodiment of the present invention;

FIG. 2 is a cross-sectional view taken along the line II-II in FIG. 1;

FIG. 3 is a cross-sectional view taken along the line III-III in FIG. 2;

FIG. 4 is a plan view showing an unfolded rotor;

FIG. 5 is a plan view showing a state where the rotor is rotated;

FIG. 6 is a cross-sectional view of a modified stopper;

FIG. 7 is a cross-sectional view of another modified stopper; and

FIG. 8 is a cross-sectional view taken along the line VIII-VIII in FIG.7.

REFERENCE NUMERALS

-   -   1 chip type variable resistor    -   2 insulating substrate    -   3 adjustment rotor    -   4 internal terminal electrode plate    -   5 through hole    -   6 resistance film    -   7, 8 external terminal electrode    -   9 shaft portion    -   10 stopper piece    -   10′ abutment piece    -   11 first plate    -   12 fold-back joint    -   12′ bending line    -   12 a portion of the fold-back joint between the bending line and        the second plate    -   12 b portion of the fold-back joint between the bending line and        the first plate    -   13 second plate    -   14 screwdriver engagement hole    -   16 sliding piece    -   19 downwardly bent lug

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of the present invention will be described below referringto the drawings, in which the present invention is applied to a chiptype variable resistor (FIGS. 1 to 5).

In these figures, the reference numeral 1 designates a chip typevariable resistor. The chip type variable resistor 1 includes aninsulating substrate 2 in the form a chip made of a heat-resistantinsulating material such as a ceramic, an adjustment rotor 3 disposed onthe insulating substrate 2, and an internal terminal electrode plate 4disposed on the lower surface of the insulating substrate 2.

The insulating substrate 2 is formed with a through hole 5 extendingfrom the upper surface to the lower surface of the substrate at agenerally central position, and a resistance film 6 disposed to extendthereon in an arcuate shape concentric with the through hole 5, and theinsulating substrate 2 is provided, on a lateral face 2 a thereof, withexternal terminal electrodes 7, 8 corresponding to the respective endportions of the resistance film 6.

The internal terminal electrode plate 4 is made of a metal and disposedin close contact with the lower surface of the insulating substrate 2,and includes a hollow shaft portion 9 integrally formed therewith to beinserted into the through hole 5, and a stopper piece 10 integrallyformed therewith to be bent upward along another lateral portion 2 b ofthe insulating substrate 2.

The rotor 3 includes a first plate 11 made of a metal plate and formedin a bowl shape with a flange around an outer periphery thereof, and aplate-shaped second plate 13 integrally connected to the first plate 11via a fold-back joint 12, and the second plate 13 includes across-shaped screwdriver engagement hole 14 perforated therethrough, andis bent to be folded back at the fold-back joint 12 thus to besuperposed on the upper surface of the first plate 11, while the flangeon the outer periphery of the first plate 11 includes a slit hole 15perforated in a generally semicircular arc in a region opposite to thefold-back joint 12, and a portion of the flange radially outer from theslit hole 15 constitutes a sliding piece 16 to be brought into elasticcontact with the resistance film 6.

The rotor 3 is mounted on the upper surface of the insulating substrate2, such that a mounting hole 18 perforated in a bottom plate 17 of thefirst plate 11 of the rotor 3 is fitted over the hollow shaft portion 9,and then the lower surface of the bottom plate 17 is closely pressedagainst the upper surface of the insulating substrate 2 and the slidingpiece 16 is set in elastic contact with the resistance film 6, afterwhich an upper end portion of the shaft portion 9 is crimped to extendoutward, so that the rotor 3 is attached to the shaft portion 9 tofreely rotate around the shaft portion 9.

A portion 12 a of the fold-back joint 12 between a bending line 12′thereof and the second plate 13 is provided with a pair of left andright downwardly bent lugs 19 integrally formed therewith, and a portion12 b of the fold-back joint 12 between bending line 12′ of the fold-backjoint 12 and the first plate 11 fits between the downwardly bent lugs19.

Also, the downwardly bent lugs 19 are formed to extend farther downwardfrom the lower surface of the portion 12 b of the fold-back joint 12between the bending line 12′ thereof and the first plate 11, and to bebutted to the stopper piece 10.

Under such structure, the rotor 3 is rotated in left and rightdirections with a screwdriver inserted into the screwdriver engagementhole 14 of the second plate 13.

In this case, the rotational force of the screwdriver is first appliedto the second plate 13, and then transmitted to the first plate 11 fromthe second plate 13.

The transmission of the rotational force from the second plate 13 to thefirst plate 11 depends, unlike the conventional resistors, notexclusively on the fold-back joint 12, but also on the pair of left andright downwardly bent lugs 19 provided to the fold-back joint 12. Sucharrangement reliably prevents the fold-back joint 12 from being deformedto incur a shift between the first plate and the second plate, with thenarrow width of the fold-back joint 12 unchanged.

Also, when the rotor 3 is rotated to left and right, the pair of leftand right downwardly bent lugs 19 of the rotor 3 is butted to thestopper piece 10 as shown in FIG. 5, thereby delimiting the rotationrange of the rotor 3 within an angle of θ.

In this case, the pair of left and right downwardly bent lugs 19 extendsfarther downward from the lower surface of the fold-back joint 12, whichallows forming the stopper piece 10, to which the downwardly bent lugs19 are butted, in a lower projecting height H from the upper surface ofthe insulating substrate 2 than in the case where the fold-back joint 12is butted to the stopper piece 10, thereby effectively increasing thestrength of the stopper piece 10 against tilting in the rotationdirection of the rotor 3 thus being deformed, without an increase inwidth of the stopper piece 10.

Besides, a portion of the internal terminal electrode plate 4corresponding to the shaft portion 9 is made thinner, and a film 20 thatcovers the inside of the shaft portion 9 is adhered to the lower surfaceof the thinner portion, to prevent intrusion of a flux produced by asoldering process into an inner portion of the rotor 3, whenimplementing the resistor on a PCB or the like by soldering.

Further as shown in FIG. 6, the stopper piece 10 may include an abutmentportion 10′, integrally formed therewith to make contact with the uppersurface of the insulating substrate 2.

With such structure, the stopper piece 10 holds the insulating substrate2 from an upper and a lower direction with the abutment portion 10′ andthe internal terminal electrode plate 4, both integrally formed with thestopper piece 10, which significantly increases the strength of thestopper piece 10 against tilting in the rotation direction of the rotor3. Besides, the internal terminal electrode plate 4 is attached to theinsulating substrate 2 at two points, namely the portion of the shaftportion 9 integrally formed with the internal terminal electrode plate 4crimped over the rotor 3, and the abutment portion 10′ integrally formedwith the stopper piece 10 holding the insulating substrate 2, whichincreases the adhesion strength of the internal terminal electrode plate4 against the insulating substrate 2.

Still further, the stopper piece may be formed in a shape having aC-shaped cross-section, as a stopper piece 10″ shown in FIGS. 7 and 8.

1. A chip type variable electronic part including an insulatingsubstrate and an adjustment rotor made of a metal plate rotatablymounted on an upper surface of the insulating substrate, the rotorincluding a first plate formed in a bowl shape to receive a screwdriverfor rotating the rotor, and a second plate superposed on an uppersurface of the first plate and integrally coupled to the first plate viaa fold-back joint, the second plate being formed with a screwdriverengagement hole into which the screwdriver is fitted, wherein thefold-back joint includes a pair of right and left downwardly bent lugsformed between a bending line of the fold-back joint and the secondplate, the bent lugs being arranged to flank a portion of the fold-backjoint that extends between the bending line and the first plate.
 2. Thechip type variable electronic part according to claim 1, wherein thepair of downwardly bent lugs extends farther downward from a lowersurface of the portion of the fold-back joint between the bending linethereof and the first plate, to be butted to a stopper piece projectingupward from an upper surface of the insulating substrate.
 3. The chiptype variable electronic part according to claim 2, wherein the stopperpiece is an upwardly bent portion of an internal terminal electrodeplate disposed on a lower surface of the insulating substrate.
 4. Thechip type variable electronic part according to claim 3, wherein thestopper piece includes an abutment portion integrally formed therewith,to be in contact with the upper surface of the insulating substrate. 5.The chip type variable electronic part according to claim 1, furthercomprising a resistance film of an arcuate shape concentric with athrough hole in the substrate, and external terminal electrodes for endportions of the resistance film, wherein the adjustment rotor isprovided with a sliding piece held in sliding contact with theresistance film.